EP0012746B1 - Telecopying process using a smectic liquid cristal cell and transceiver telecopier for application of said process - Google Patents

Abstract

A teleprinting process and a transceiver teleprinter for application of said process. It is proposed to use during the receiving phase a smectic liquid cristal cell for recording by a thermo-optic process of an intermediary image of a linear element (fragment of column or complete line) of the transmitted document, image which is then projected onto a photosensitive surface. The same optic system allows, at the transmitting phase, the reading of this linear element by a mosaic of detectors and, at the receiving phase, the projection onto the photosensitive surface of the intermediary image recorded in the cell. The invention is applicable to teleprinting through the channel of an ordinary telephone network or of high flow transmission lines, as well as to information transmission by compression.

Description

The present invention relates to a transceiver facsimile machine, and more particularly a facsimile machine using a film of mesomorphic material having a smectic phase for the intermediate recording of a linear element of the document to be faxed, this intermediate recording then being projected onto a photosensitive surface. The device is designed to operate, both on transmission and on reception, coupled both to the ordinary telephone network and to high speed data transmission lines.

Almost all of the fax machines currently in use use direct registration. The video signal, resulting from the point by point and line by line analysis of the document to be faxed, is applied to an electrode having the shape of a fine point, which moves in the immediate vicinity of a sensitive paper to write a succession of points. Printing of the paper is obtained by various methods. The paper can be provided with an underlying conductive layer formed of carbon black or of an electrolyte; in the first case, a voltage applied to the tip generates a spark which pierces the paper and causes carbon black to appear; in the second case, the current from the tip causes the migration of colored metal ions to the surface of the paper. A heat-sensitive paper, obtained by impregnation of fatty acid salts decomposable by heat, can also be used; the flow of current heats the tip and the metal released colors the paper. Other systems use the tip to deposit by Corona effect on a paper coated with a dielectric layer, point electrical charges which allow subsequent fixing of a coloring powder called "toner". All of these processes are ill-suited to reproducing halftones. In addition, the size of the point and the effects used limit the fineness of the points, therefore the definition of the document reproduced, to values of the order of 3 to 4 points per mm.

Furthermore, it is known to use thin films of mesomorphic materials, also known as liquid crystals, to display information transmitted in the form of a video signal.

Thus, it has been proposed in a patent entitled "Display device for television receiver filed in France on August 6, 1970 by RCA Corporation and published under the number 2.057.035. to use in a telereprography system a linear cell containing a liquid crystal material in nematic phase. The document to be transmitted is analyzed line by line by a Vidicon tube. On reception, the video signal thus transmitted is put in memory line after line, the N signals corresponding to the N points of a line being applied simultaneously to the N elements of the cell whose diffusivity they modulate while the signals corresponding to the next line. The image of the cell, lit by a light source, is projected onto a photosensitive surface. The inscription in the reading crystal material and its projection on the photosensitive surface are thus simultaneous.

In a patent entitled: "Locally erasable thermooptic smectic liquid-crystals storage displays", filed in the USA on October 19, 1972 and issued on March 12, 1974 under number 3,796,999, FJ KAHN proposed to scan a film maintained in the smectic phase by a beam of infrared light modulated in intensity. The film is initially in an ordered structure, therefore transparent. The thermal energy communicated to the points of the film irradiated by the beam at its maximum intensity is sufficient to cause them to temporarily transit from the smectic phase into the isotropic liquid phase. By rapidly returning to the initial temperature corresponding to the smectic phase, these points take on a macroscopically disordered structure, known as a focal conic, which is diffusing. The information thus recorded in the film remains stable for several hours; to erase it, the film is brought back to the liquid phase, then cooled slowly until the smectic phase where it resumes an ordered transparent structure. The device does not lend itself well to writing halftones, and a significant part of the energy of the light beam is lost in the modulator.

In the French patent entitled: "Device for reproducing black and white images using a material having a smectic phase and teletransmission and telereprography system using this device _" , filed by the Applicant on June 14, 1974 and issued on February 13 1976 under number 2.275.087, it was proposed to enclose the film in the smectic phase between two transparent electrodes, between which the video signal is applied. An infra-red beam of constant intensity scans the layer in synchronism with this signal The scanned points are thus subjected, during their cooling from the liquid phase to the smectic phase to an electric field of variable intensity. The restructuring of the film into an ordered structure, zero in the absence of field, is all the more pronounced that the latter is more intense. The video signal thus modulates the diffusivity of the scanned points. This device provides an inscription with halftones and saves the use of a n electro-optical modulator. Nevertheless, obtaining high writing speeds entails the use of highly directive and very powerful infrared sources; such sources, as well as the beam deflectors which accompany them, also constitute bulky and costly members.

In this same patent, it is also proposed to use the memory effect presented by the image reproduction device for an application to telereprography. The recording of the transmitted document is then indirect and carried out in two stages: in a first stage an entire page of the document is displayed in the smectic layer, then, in a second step, projected onto a photosensitive surface. However, the device described above, if it makes it possible to obtain an excellent definition of the transmitted document, implements, as already indicated, bulky and expensive equipment. In addition, it hardly lends itself to coupling with the transmitter part essential to any facsimile device.

Finally, it is also known to control a liquid crystal display cell by multiplexing. For example, in a patent entitled "Method and device using a thermo-optical effect in a liquid crystal for the reproduction of images in real time and without memory" filed by the Applicant on November 21, 1974 and published under the N ° 2.292.253, a device is described making it possible to selectively heat a layer of nematic liquid crystal by means of a matrix of resistors controlled by multiplexing.

The object of the present invention is to provide a fax machine which overcomes the drawbacks of the known art and which, while being both a transmitter and a receiver, is of low cost price and nevertheless allows reproduction of the documents transmitted with halftone and high definition, and possibly a high reproduction speed compatible with high speed data lines.

To achieve this result, the present invention uses an intermediate recording in a liquid crystal layer, a method which has the advantage, compared to direct recording methods, of allowing reproduction with a higher definition and halftones.

The invention also proposes to perform this intermediate recording in a liquid crystal in the smectic phase, which makes it possible to obtain a contrast greater than that which a recording in a material in the nematic phase would provide. In addition, the fact that a recording in smectic phase is a recording with memory, property which does not exist for the recordings in nematic phase, was taken advantage, in one of the embodiments described, to obtain a very definition high of the reproduced document without having to resort to an important connection.

This being the case, the invention had to face the problem of intermediate registration in a smectic layer. The use of a laser to heat the layer point by point was difficult to envisage, for reasons of space, energy consumption and cost. This problem has been solved by using a method which consists in simultaneously heating a rectilinear segment of the smectic layer corresponding to a high number of discrete points by a voltage pulse applied to a heating resistor in contact with the layer; during the subsequent cooling of the latter, the control voltages corresponding to the different points, previously stored in a memory from the video signal received by the facsimile machine, are applied simultaneously to the entire segment. The invention also proposes to have a number of such segments end to end. and order them by multiplexing, in order to display an entire line with very high definition.

Finally, the invention proposes to combine in a single optical device the linear liquid crystal cell intended for intermediate registration in the reception operation of the fax machine, and a photodetector array making it possible to read the document to be transmitted in the operation in emission, the passage from one operating mode to another being done by simple tilting of a plane mirror.

• Figure 1 : une vue schématique du télécopieur suivant l'invention ;
• Figures 2a, 2b, 2c : la constitution des moyens d'affichage intermédiaires, constitués par une cellule à matériau mésomorphe dans un premier exemple de réalisation selon l'invention, à savoir respectivement, une fente-diaphragme déposée sur la face externe d'une des lames de la cellule, une résistance chauffante transparente disposée sur la face interne de cette même lame, et P électrodes transparentes disposées sur la face interne de l'autre lame ;
• Figure 3 : l'agencement de P détecteurs constituant une mosaïque linéaire de détecteurs et du générateur de commande associé à cette mosaïque, dans ce premier exemple de réalisation selon l'invention ;
• Figure 4 : un schéma montrant comment s'effectue la lecture d'une page de document à télécopier dans ce premier exemple de réalisation selon l'invention ;
• Figure 5 : un diagramme montrant la synchronisation des impulsions de tension de commande, de chauffage et de lumière dans ce premier exemple de réalisation selon l'invention :
• Figure 6 : l'agencement de P x Q détecteurs constituant une mosaïque linéaire de détecteurs et du générateur de commande de lecture par multiplexage associé à cette mosaïque dans un second exemple de réalisation selon l'invention ;
• Figures 7a et 7b : la constitution de la cellule d'affichage, à savoir les dispositions respectives de Q résistances chauffantes et de P x Q électrodes, et des moyens de commande par multiplexage qui leur sont associés, dans ce même second exemple de réalisation selon l'invention.

Other features and advantages of the invention will appear clearly in the description below, presented by way of nonlimiting example. The attached figures represent:

• Figure 1: a schematic view of the facsimile machine according to the invention;
• Figures 2a, 2b, 2c: the constitution of the intermediate display means, constituted by a cell with mesomorphic material in a first embodiment according to the invention, namely respectively, a diaphragm slot deposited on the external face of a blades of the cell, a transparent heating resistor arranged on the internal face of this same blade, and P transparent electrodes disposed on the internal face of the other blade;
• Figure 3: the arrangement of P detectors constituting a linear mosaic of detectors and of the command generator associated with this mosaic, in this first example of embodiment according to the invention;
• FIG. 4: a diagram showing how a page of document to be faxed is read in this first exemplary embodiment according to the invention;
• Figure 5: a diagram showing the synchronization of the control voltage, heating and light pulses in this first exemplary embodiment according to the invention:
• FIG. 6: the arrangement of P × Q detectors constituting a linear mosaic of detectors and of the reading control generator by multiplexing associated with this mosaic in a second exemplary embodiment according to the invention;
• Figures 7a and 7b: the constitution of the display cell, namely the respective arrangements of Q heating resistors and P x Q electrodes, and of the multiplexing control means associated with them, in this same second embodiment according to the invention.

We can see in Figure 1 a schematic representation of the transceiver facsimile according to the invention.

• - des moyens d'éclairement comprenant une source lumineuse rectiligne 100. un réflecteur 101. un condensateur 102 et une rente-diaphragme 103 ;
• - des moyens d'affichage linéaire intermédiaire constitués par la cellule à cristal liquide 11. disposée au voisinage immédiat du diaphragme 103 ;
• - une mosaïque linéaire de photodétecteurs 12, de dimensions identiques à celles de la fente diaphragme 103 ;
• - des moyens de projection comprenant un miroir plan fixe et semi-transparent 130, un objectif de projection 131 muni d'un diaphragme variable 132 et un miroir plan 133, mobile autour d'un axe 134 perpendiculaire au plan de la figure ;
• - une surface photosensible mobile 14 ;
• - des moyens de positionnement 15 du document à photocopier.

This device comprises as optical and optoelectronic organs:

• - lighting means comprising a rectilinear light source 100. a reflector 101. a capacitor 102 and a diaphragm annuity 103;
• - Intermediate linear display means constituted by the liquid crystal cell 11. disposed in the immediate vicinity of the diaphragm 103;
• - A linear mosaic of photodetectors 12, of dimensions identical to those of the diaphragm slot 103;
• - projection means comprising a fixed and semi-transparent plane mirror 130, a projection lens 131 provided with a variable diaphragm 132 and a plane mirror 133, movable around an axis 134 perpendicular to the plane of the figure;
• - a movable photosensitive surface 14;
• - Positioning means 15 of the document to be photocopied.

The liquid crystal cell 11 is shown in Figure 1 in a sectional view made perpendicular to its largest dimension. It has two transparent solid blades 20 and 21, parallel and separated from each other by two shims 210 and 201. The space provided between the blades 20 and 21 and the shims 210 and 201 is filled with a layer 3 of a mesomorphic material having a smectic phase. References 3i and 3ij relate to two transparent conductive deposits partially lining the internal faces of the blades 20 and 21 and acting respectively as one against electrode and heating resistance and the other as electrode. The cell 11 comprises at least one set of P electrodes and at least one heating resistor.

qui présente entre 20 et 32,5 °C une phase smectique A et dont la transition nématique-liquide isotrope s'effectue à 40°5. Un dispositif thermostatique, non représenté sur la figure, maintient si besoin en est, le matériau mésomorphe, en l'absence de courant dans la ou les résistances chauffantes, à une température légèrement inférieure à la température de transition smectique-nématique. Eventuellement, les surfaces des dépôts conducteurs et des lames en contact avec le matériau mésomorphe peuvent être traitées par des procédés connus pour permettre un retour spontané, mais relativement lent, de ce dernier en phase ordonnée transparente ; on peut en particulier utiliser des surfactants appropriés, notamment le produit connu sous le nom de « Silane qui est d'un emploi étendu et convient parfaitement lorsque le matériau mésomorphe est le C. O. B. précédemment cité.By way of example, glass or sapphire can be used to form the blades 20 and 21 and tin oxide (SnO ₂ ) or indium (ln0 ₂ ), or a mixture of these two oxides, for conductive deposits 11 and 12. The strips 20 and 21 are spaced 10 to 20 µ apart. Good results are obtained by using, as a mesomorphic material, compounds from the cyano-biphenyl family, alone or as a mixture, and in particular cyano-octyl-biphenyl (COB) corresponding to the formula

which has a smectic phase A between 20 and 32.5 ° C and whose nematic-isotropic liquid transition takes place at 40 ° 5. A thermostatic device, not shown in the figure, maintains, if necessary, the mesomorphic material, in the absence of current in the heating element or resistors, at a temperature slightly lower than the smectic-nematic transition temperature. Optionally, the surfaces of the conductive deposits and of the blades in contact with the mesomorphic material can be treated by known methods to allow spontaneous, but relatively slow, return of the latter in the transparent ordered phase; it is possible in particular to use suitable surfactants, in particular the product known under the name of “Silane which is of widespread use and is perfectly suitable when the mesomorphic material is the COB mentioned above.

The light source 100 is for example a source with a straight filament, arranged perpendicular to the plane of FIG. 1. The capacitor 102 forms the image of the source 100 in the plane of the diaphragm 103. The plane mirror 133 may have its reflecting surface directed either towards the photosensitive surface 14 (position “reception shown in solid lines in FIG. 1), or towards the positioning means 15 to the document to be photocopied (position“ emission represented in dotted lines), so as to project into the plane of the either of these surfaces the image of the diaphragm slot 103 provided by the lens 131.

The capacitor 102 has a relatively small digital aperture, f / 6 or f / 8 for example. The digital aperture of the lens 131 is determined by the diaphragm 132, the aperture of which is linked to the position of the mirror 133. When the mirror is in the “reception” position, the aperture of the diaphragm 132 is just sufficient to allow passage the light flux emanating from the capacitor 102 after crossing the diaphragm 103, in the absence of any scattering caused by the cell 11. On the contrary, when the mirror 133 is in the emission position ", the diaphragm 132 is wide open, so as to leave lens 131 work at full aperture.

The photosensitive surface 14 may consist of a paper coated with a silver emulsion, for example a hot-developing paper. It can also be a layer of a photoconductive material, selenium or zinc oxide for example, used according to techniques known in electrostatic photocopying. The device for developing, fixing and possibly transferring recorded information, a device which belongs to the known art, has not been shown in FIG. 1. The linear mosaic of detectors 12 is arranged symmetrically at layer 3 with respect to the semi-transparent mirror 130 and is thus, when the plane mirror 133 is in the "emission" position, in the conjugate plane of the document to be photocopied maintained by the positioning means 15.

• - un modulateur mécanique, composé d'un disque muni de fentes radiales, interposé au voisinage de la source 100, entre cette dernière et l'objectif 102, et actionné par un moteur 105 ;
• - un premier système moteur 106 permettant de translater l'ensemble constitué par les moyens d'éclairement 100, 101 et 102, le modulateur 104 et 105, le diaphragme 103, la cellule 11, le miroir semi-transparent 130, le détecteur 12 et l'objectif 131. Ce déplacement, qui s'effectue suivant une direction perpendiculaire tant à l'axe optique commun des objectifs 102 et 131 qu'à l'axe 134 de rotation du miroir 133, permet de déplacer l'image de la source lumineuse 100 vue à travers la fente diaphragme 103 soit dans le plan de la surface photosensible 14, soit dans le plan des moyens de positionnement 15, selon la position du miroir 133 ;
• - un second système moteur 135 commandant la rotation du miroir 133 pour lui permettre d'occuper l'une ou l'autre des deux positions « réception » et « émission » précédemment mentionnées, toutes deux à 45° de l'axe optique commun aux deux objectifs 102 et 131. Eventuellement, ce même système moteur commande un déplacement continu ou pas à pas du miroir 133 de part et d'autre des deux positions moyennes définies ci-dessus, de telle sorte que l'image de la source 100 balaye les surfaces 14 ou 15 ; le système moteur 106 qui, assumant la même fonction, devient inutile, est alors supprimé ;
• - un troisième système moteur, permettant le déplacement de la surface photosensible 14. La figure 1 concerne plus spécialement le cas où la surface photosensible 14 est une émulsion argentique disposée sur un rouleau de papier 140, la feuille étant progressivement entraînée par les deux presseurs circulaires 141, 142 entraînés par le moteur 143 ; dans l'exemple décrit, le déplacement de la surface 14 s'effectue perpendiculairement à l'image de la source 100 vue à travers la fente diaphragme 103. Selon une variante de l'invention, le déplacement de la surface 14 peut également s'effectuer parallèlement à l'image de la source 100. La surface photosensible 14 peut être également disposée sur une surface cylindrique en rotation autour de son axe, axe qui est alors disposé parallèlement à l'image de la source ; un tel arrangement est utilisable notamment lorsque l'on utilise un matériau photoconducteur selon une technique connue de la copie électrostatique ;
• - un quatrième système moteur 15 assurant la translation, suivant une direction perpendiculaire au plan de la figure, des moyens de positionnement 15 ;
• - un système de commande 136 de l'ouverture du diaphragme 132.

The facsimile machine of FIG. 1 also has the following mechanical components:

• - A mechanical modulator, composed of a disk provided with radial slots, interposed in the vicinity of the source 100, between the latter and the objective 102, and actuated by a motor 105;
• a first motor system 106 making it possible to translate the assembly constituted by the lighting means 100, 101 and 102, the modulator 104 and 105, the diaphragm 103, the cell 11, the semi-transparent mirror 130, the detector 12 and objective 131. This displacement, which takes place in a direction perpendicular to both the common optical axis of the objectives 102 and 131 and to the axis 134 of rotation of the mirror 133, makes it possible to move the image of the light source 100 seen through the diaphragm slot 103 either in the plane of the photosensitive surface 14, either in the plane of the positioning means 15, according to the position of the mirror 133;
• a second motor system 135 controlling the rotation of the mirror 133 to allow it to occupy one or the other of the two positions “reception” and “emission” previously mentioned, both at 45 ° from the optical axis common to the two objectives 102 and 131. Optionally, this same motor system controls a continuous or step-by-step movement of the mirror 133 on either side of the two average positions defined above, so that the image of the source 100 scans surfaces 14 or 15; the engine system 106 which, assuming the same function, becomes useless, is then deleted;
• - A third motor system, allowing the displacement of the photosensitive surface 14. FIG. 1 relates more particularly to the case where the photosensitive surface 14 is a silver emulsion placed on a roll of paper 140, the sheet being gradually driven by the two circular pressers 141, 142 driven by the motor 143; in the example described, the displacement of the surface 14 takes place perpendicular to the image of the source 100 seen through the diaphragm slot 103. According to a variant of the invention, the displacement of the surface 14 can also be perform parallel to the image of the source 100. The photosensitive surface 14 can also be arranged on a cylindrical surface in rotation about its axis, an axis which is then arranged parallel to the image of the source; such an arrangement can be used in particular when using a photoconductive material according to a known technique of electrostatic copying;
• - A fourth motor system 15 ensuring the translation, in a direction perpendicular to the plane of the figure, of the positioning means 15;
• a control system 136 for opening the diaphragm 132.

• - un bloc logique de commande 16 comportant un contacteur à deux positions « émission « réception et munie d'une horloge pilote ; ce bloc contrôle le système de commande 136 du diaphragme 132 et, par le moteur 135, la position « émission » ou « réception » du miroir 133 ; il émet en outre des signaux permettant de synchroniser: à l'émission, le mouvement des moteurs 106 ou 135 assurant le balayage lumineux du document à télécopier disposé en 15, le mouvement du moteur 151 déplaçant ce même document et le fonctionnement des moyens photodétecteurs linéaires 12 ; à la réception, le mouvement du moteur 105 entraînant le disque modulateur 104, le mouvement des moteurs 106 ou 135 assurant le balayage lumineux de la surface photosensible disposé en 14, le mouvement du moteur 143 assurant le déplacement de cette même surface 14 et le fonctionnement de la cellule 11 ;
• - un générateur de commande de lecture 170 recevant lors de la phase « émission », les impulsions de commande de provenance du bloc logique 16 et commandant la lecture de la mosaïque linéaire de photodétecteurs 12 ; ce générateur de commande envoie vers la ligne de transmission, par le canal de l'amplificateur 171, et d'un éventuel système de compression de l'information, non représenté sur la figure, le signal S_L qui comporte l'information lue par les détecteurs, et les signaux de synchronisation lignes et images ;
• - un amplificateur sélecteur 180 qui reçoit et amplifie le signal S_R en provenance de la ligne de transmission, et en extrait les impulsions de synchronisation vers la logique 16 ;
• - un échantillonneur 181, sous la commande du bloc logique 16, échantillonne le signal vidéo en provenance de l'amplificateur 180 en une série d'impulsions de tension de commande distinctes à fréquence constante ;
• - un convertisseur-série-parallèle 182 également commandé par le bloc logique 16 met en mémoire les impulsions successives reçues de l'échantillonneur 181 et les applique simultanément, à intervalles de temps régulièrement espacés, par paquets de P, aux ensembles de P électrodes telles que l'électrode 3ij de la cellule 11 ; les électrodes de rang 1 de chaque ensemble reçoivent ainsi simultanément la première impulsion de tension de commande V_C1 emmagasinée par la mémoire, les électrodes de rang 2 la deuxième V_cz... et les électrodes de rang P la Pème impulsion V_cp. Si la compression de l'information est utilisée pour la transmission du document, la partie réception du télécopieur doit comporter une mémoire tampon de deux à trois lignes de capacité minimale. Cette mémoire tampon constitue alors la mémoire du convertisseur série parallèle 182.
• - un générateur d'impulsions de chauffage 190, qui comporte autant de sorties qu'il y a de résistances chauffantes telles que 3i dans la cellule 11 pour délivrer à ces dernières, sous la commande du bloc logique 16, des impulsions de chauffage I_c1, I_C2, ..., I_co régulièrement espacées dans le temps, en synchronisme avec les impulsions de tension de commande appliquées aux électrodes.

Finally, the device of FIG. 1 comprises a certain number of electronic circuits, in particular:

• - A control logic block 16 comprising a two-position "send" receive switch and provided with a pilot clock; this block controls the control system 136 of the diaphragm 132 and, by the motor 135, the "emission" or "reception" position of the mirror 133; it also transmits signals making it possible to synchronize: on transmission, the movement of the motors 106 or 135 ensuring the light scanning of the document to be faxed arranged at 15, the movement of the motor 151 moving this same document and the operation of the linear photodetector means 12; on reception, the movement of the motor 105 driving the modulating disc 104, the movement of the motors 106 or 135 ensuring the light scanning of the photosensitive surface arranged at 14, the movement of the motor 143 ensuring the displacement of this same surface 14 and the operation from cell 11;
• a reading command generator 170 receiving during the "emission" phase, the command pulses from the logic block 16 and controlling the reading of the linear mosaic of photodetectors 12; this command generator sends to the transmission line, via the channel of the amplifier 171, and of a possible information compression system, not shown in the figure, the signal S _L which includes the information read by detectors, and line and image synchronization signals;
• - a selector amplifier 180 which receives and amplifies the signal S _R coming from the transmission line, and extracts from it the synchronization pulses towards the logic 16;
• a sampler 181, under the control of the logic block 16, samples the video signal coming from the amplifier 180 in a series of distinct control voltage pulses at constant frequency;
• a serial-parallel converter 182 also controlled by the logic block 16 stores the successive pulses received from the sampler 181 and applies them simultaneously, at regularly spaced time intervals, in packets of P, to the sets of P electrodes such that the electrode 3ij of cell 11; the row 1 electrodes of each set thus simultaneously receive the first control voltage pulse V _C1 stored by the memory, the row 2 electrodes the second V _cz ... and the row P electrodes the P th pulse V _c p. If compression of the information is used for the transmission of the document, the reception part of the fax machine must include a buffer memory of two to three lines of minimum capacity. This buffer memory then constitutes the memory of the parallel serial converter 182.
• a heating pulse generator 190, which has as many outputs as there are heating resistors such as 3i in the cell 11 for delivering to the latter, under the control of logic block 16, heating pulses I _c1 , I _C2 , ..., I _co regularly spaced in time, in synchronism with the control voltage pulses applied to the electrodes.

Figures 2 to 5 relate to a first embodiment of the device shown in Figure 1, more specifically intended to work with a conventional telephone network provided with an information compression device. The essential characteristic of this first example is that a set of P lines of the document to be faxed is read and written in parallel.

FIGS. 2a, 2b and 2c show the constitution of the cell 11 and respectively represent the external face, of the blade 20, the internal face of this same blade 1 and the internal face of the blade 21.

As shown in FIG. 2a, the external face of the blade 20, which constitutes the external part of the cell directed towards the light source 100 comprises an opaque coating 200, constituted by a metallic deposit, in which is formed a rectilinear slot 103 leaving the surface of the transparent blade bare and which constitutes the diaphragm slot previously mentioned and designated under the same reference in figure 1.

FIG. 2b shows the configuration of the transparent conductive deposit 31 deposited on the internal face of the blade 20, to constitute a single heating resistor; this deposit forms an elongated strip, of dimensions slightly greater than those of the slot 103 disposed on the other face of the blade (shown in punctuated lines in FIG. 2a) which it completely covers. One of the ends of the deposit 31 is connected to ground, the other receives the pulses I _C1 delivered by a single output of the generator 190.

FIG. 2c shows the configuration of the transparent conductive deposits 311, 312 ... 31P which constitute the single set of P identical electrodes lining the internal face of the blade 21. In this figure, the position occupied by the slot 103 when the cell is assembled has been shown in dotted lines to allow the respective positions in the cell of slot 103, of the heating resistance against electrode 31 and of electrodes 311 to 31 P to be located. It can be seen that these electrodes line the entire length of the surface located opposite the heating resistance, and have substantially the same length as the latter. They simultaneously receive from the serial-parallel converter 182 the control voltage pulses V _C1 , V _c2 , ... V _c p.

FIG. 3 shows the arrangement, in this first embodiment, of the linear mosaic of detectors 12, and of the reading control generator 170 which is associated with it.

The mosaic 12 comprises P identical aligned photo-conductive detectors 121, 122, ... 12P, or as many elements as there are electrodes 311, ..., 31 P in the cell 11. The punctuated lines represent the magnification image 1 of the diaphragm slot 103, projected in the plane 15 by the lens 131 and reprojected by this same lens and the semi-transparent mirror 130, in the plane of the linear mosaic 12. The sensitive surfaces of the detectors are aligned to cover the entire image.

The control generator 170 comprises a voltage source E, connected to a common terminal of the detectors, P switches I ₁ , I ₂ , ..., I _P each allow to connect to ground, by the channel of a resistance of common load R, the other terminal of the detector corresponding to a control block C triggering, as a function of the signal received from the logic block 16, the momentary closing successively of each switch. The read signal, taken upstream of the resistor R, is sent to the input of the amplifier 171.

The operation of the fax machine, according to this first exemplary embodiment, is carried out as follows:

Putting on position “emission of the logic block 16 causes the triggering of a heating pulse applied to the heating resistor 31; the heat released temporarily carries the layer 3 of mesomorphic material from the smectic phase to the isotropic liquid phase; during the subsequent return of layer 3 to the smectic phase, the logic block 16 triggers, via circuits 181 and 182, P identical control voltage pulses, of maximum value, which are applied to P electrodes 311 ... 31 P of the cell and cause the uniform orientation, for an indefinite time, of the layer 3. The cell 11 is then uniformly transparent.

Simultaneously, the logic block 16 has put the modulator 104 at a standstill in a position allowing the light coming from the source 100, opened the diaphragm as much as possible 132, put the mirror 133 in the "emission" position, then triggered the scanning. of the document arranged at 15 by starting either the motor 106 or the motor 135 depending on the version chosen.

The image of the source 100, projected by the capacitor 102, illuminates the diaphragm slot 103, the image of which is projected by the objective 131 and the mirror 133, on the document to be photocopied placed in the positioning means 15. As shown in Figure 4, the light segment thus formed illuminates the upper left corner of the document to be faxed and sweeps it in a continuous movement in the direction "lines" from left to right in the direction indicated by the arrow f _i . When the light segment has reached the extreme right edge, the logic block 16 starts the stepping motor 151 which moves the positioning means 15 in the direction indicated by the arrow F ₁ (direction "colonhes") by a length equal to that of the light line, then reverse the movement of the 106 or 135 motors; the scanning "lines then starts in the opposite direction, in the direction indicated by the arrow F ₂ . The two alternating movements continue until the light line has swept the entire page.

• v = g · l₁/t₁.

The objective 131 re-forms, via the semi-transparent mirror 130, the image of the illuminated part on the linear mosaic of detectors 12. The resistance of each element is modulated as a function of the illuminance received, which depends on the more or less great absorption, vis-à-vis the light radiation, of the corresponding point of the document to be transmitted arranged in the plane 15. The command generator 170 makes it possible to successively read, always in the same order, the variations in resistance of the photoconductors 121, ..., 12P, which appear in the form of voltage variations across the resistor R. These variations, amplified by the amplifier 171, constitute the transmitted signal S _L. Reading the matrix requires a time t ₁ , at the rate of t _l / P per element. If 1 ₁ is the width of the slit-diaphragm 103, and g the linear magnification of the objective 131, the speed of movement v of the light line in the plane 15 will be adopted:

• v = g · l ₁ / t ₁ .

• N_L=L₁/g·l₁;
• N_C =P·L₂/g · I₂

(I₂ étant la longueur de la fente-diaphragme 103). P lignes du document sont ainsi lues simultanément. Le temps mis par le dispositif pour lire simultanément les P lignes est :

• T_L = t₁ L_l/g L₁

et le temps de lecture d'une page :

• T = t₁ L₁ L₂/g² · l₁ L₁.

A document page, of width L ₁ and of length L ₂ is thus analyzed in the form of N _L Ne independent points, the number of points per line N _L and of lines per page Ne being respectively:

• N _L = L ₁ / g · l ₁ ;
• N _C = P · L ₂ / g · I ₂

(I ₂ being the length of the diaphragm slot 103). P lines of the document are thus read simultaneously. The time taken by the device to read the P lines simultaneously is:

• T _L = t ₁ L _l / g L ₁

and the reading time of a page:

• T = t ₁ L ₁ L ₂ / g ² · l ₁ L ₁ .

Putting the logic block 16 in the “reception” position causes the diaphragm 132 to close on the minimum opening and puts the mirror 133 in the “reception” position. A “start of reading” pulse supplied by the reading facsimile machine starts the motor 105 of the mechanical modulator 104 and the motors 106 or 135 enabling the photosensitive surface 14 to be scanned.

The signal S _R received by the amplifier 180, then cut into pulses of frequency P / t ₁ by the sampler 181, is stored in memory by series of P pulses in the serial-parallel converter 182.

• - dans la partie supérieure les variations de tension appliquées par le générateur d'impulsions de chauffage 190 aux bornes de la résistance chauffante 31 ;
• - dans les parties intermédiaires les impulsions de tension de commande appliquées par le convertisseur série-parallèle 182 aux électrodes 311, 312 ..., 31P ;
• - dans la partie inférieure, les variations d'intensité lumineuse reçues au niveau de la fente-diaphragme 103, en provenance de la source lumineuse 100 à travers le modulateur 104.

The diagram in FIG. 5 shows how this converter 182 applies these pulses to the electrodes of cell 11, in synchronism with the heating pulses and the light pulses, all under the control of logic block 16. It represents as a function of time t :

• - in the upper part the voltage variations applied by the heating pulse generator 190 at the terminals of the heating resistor 31;
• - in the intermediate parts, the control voltage pulses applied by the series-parallel converter 182 to the electrodes 311, 312 ..., 31P;
• in the lower part, the variations in light intensity received at the level of the diaphragm slot 103, coming from the light source 100 through the modulator 104.

The generator 190 sends into the resistor 31, at the frequency 1 / t _l , a heating pulse of duration t ₁ / r (where r is greater than unity) which, causing the layer 3 to pass from the smectic phase to the phase isotropic liquid, erases all previously recorded information.

As soon as this pulse is finished, the converter 182 simultaneously applies each of the P pulses previously stored in memory to the P electrodes 311, ..., 31P, which thus receive control voltages respectively proportional to the signals delivered by the detectors 121, 122, ..., 12P of mosaic 12 of the sending fax machine. These pulses are applied at the frequency 1 / t ₁ for a duration: mt _l / r (m being greater than unity and less than r).

The counter-electrode and heating resistor 31 then being grounded, the electrodes generate, in the corresponding elements of the mesomorphic layer 3 which all pass from the liquid phase to the smectic phase, electric fields proportional to the voltage applied to the corresponding electrode; a field lower than a threshold value involves the return to a disordered smectic structure, therefore diffusing, and the maximum field the return to an ordered structure, therefore transparent. The linear cell 11 thus reproduces, in the form of variations in the diffusion coefficient, the variations in brightness of the column element of the transmitted document as they are measured by the mosaic 12 of the transmitting facsimile machine. These variations in the diffusion coefficient remain until erased by the next heating pulse.

When the control voltage pulses have ended, the mechanical modulator 104 unmasks the light source 100, which illuminates the diaphragm slot 103. Those of the elements of layer 3 which are in the ordered smectic phase, therefore non-diffusing, do not modify the path of the incident light beam, which passes in its entirety through the diaphragm 132; the photosensitive layer 14 receives for these points the maximum illumination. On the other hand, the more the structure of the elements of layer 3 is disordered, the more these elements are diffusing and send a large fraction to the light flux having passed through the diaphragm slot 103 outside the opening of the diaphragm 132, opening which, as before indicated is, in the "reception" position, just sufficient to let the undistributed stream pass; it follows that the photosensitive layer receives all the less light energy as the corresponding point of the intermediate display means constituted by the cell 11 is more diffusing. The light pulses, which also repeat at a frequency 1 / t _I , have a duration (r - m - 1) t ₁ / r.

Each light pulse allows the recording by the photosensitive surface of a column segment comprising P points. After N _L pulses, P consecutive lines of the transmitted document were thus recorded. A line synchronization signal from the transmitter triggers the stepping motor 143, which advances the photosensitive surface 14 by a length equal to that of the image of the P points forming the column segment. The scanning motors 106 or 135 then reverse their direction of travel, for recording the following P lines. Contrary to what is shown in FIG. 1, the displacement of the photosensitive surface 14 takes place in a direction perpendicular to the plane of the figure.

By way of practical example, the diaphragm slot 103 has a rectangular opening of width I ₁ = 25 10 ^-3 mm and of length I ₂ = 100 mm. The electrodes 311, ..., 31 P and the photodetectors 211, .., 21 P are P = 20, their width is 30 µm, their length (oriented in the direction of the length of the slot 103) 45 µm, the spacing between two consecutive electrodes being 5 µm. The heating resistor 31 has a length of 1.05 mm, a width of 30 μm; the quotient of its resistivity by its thickness has a value RO = 12 Ω; the resistance of element 31 is therefore of the order of 400 Ω. The heating pulses have a frequency of 1000 Hz, ie t = 1 ms; the pulse durations: heating, control voltage and light are respectively 0.1 ms (r = 10), 0.7 ms (m = 7) and 0.2 ms. Objective 131 works at a magnification g = 5.

Under these conditions, a typed page, format 21 x 27 cm ² is transcribed with a high definition of N _L = 1,680 dots / line and N _{c =} 1,080 lines / page, for a total of 1,810 ⁶ dots / page. Taking into account that the device makes it possible to register a column segment of 20 points in 1 ms, the registration of an entire page requires approximately 90 s. This writing speed is compatible with the transcription speed of a normal telephone line (2400 baud) working in information compression without transmitting the halftones.

Figures 5 and 6 relate to a second embodiment of the invention, for obtaining a transmitted document having a definition as high as the first, but with a higher speed. This device is designed to be coupled to a high speed data transmission line. The cell 11 in FIG. 1 is designed to display an entire line of the transmitted document and its control, as well as that of the linear mosaic of detectors 12, is carried out by multiplexing.

FIG. 6, relating to the “emitter of the device” part, shows the arrangement of a linear mosaic of photo-detectors comprising Q sets of each P photo-conductors, where, to simplify the description, the values of P and Q have been reduced to P = 4 and Q = 3. It also shows the diagram of the associated control generator 170, which reads the photoconductors by multiplexing.

The 12 detectors 211 to 214, 221 to 224 and 231 to 234 are aligned, regularly spaced, to cover the image of the diaphragm slot 103, supplied, as in the first version, by the lens 131 and the semi-mirror transparent 130. The first terminals of the photoconductors of the same assembly 211 to 214, 221 to 224 or 231 to 234 are interconnected; they are connected by three separate lines to the same pole of a voltage generator E ₁ by the channel of three switches J ¹ , J ² and J ³ , electrically controlled by a control block C ₁ , controlled by the signal from the logic block 16. The switches J ¹ , J ² , J ³ , the generator E ₁ and the control block C ₁ are part of the control generator 170; Also included are four other switches J ₁ , J ₂ , J ₃ and J ₄ , also electrically controlled by the block C ₁ , and a common load resistor R ₁ . The second terminals of the row 1 photo-conductors of each set, namely the photo-conductors 211, 221 and 213 are interconnected and flow on the resistor R ₁ through the channel of the switch J ₁ ; the same goes for the second terminals of the photoconductors of rank 2: 212, 222 and 232 by the channel of the switch J ₂ , those of the photoconductors of rank 3: 213, 223 and 233 by the channel of the switch J ₃ and those of rank 4: 214, 224 and 234 through the channel of switch J ₄ . The signal read by the photoconductors is taken from the upstream terminal of the resistor R ₁ and sent to the input of the amplifier 171.

The length of the diaphragm slot 103 and the magnification g of the objective 131 being calculated so that the image of the slot 103 covers a line of the document to be faxed, the linear mosaic 12 makes it possible to read point by point the whole of this same line. For this purpose, the block Ci now closed the only switch J ¹ , commands the closing, during equal time intervals, successively of the switches J ₁ , J ₂ , J ₃ and J ₄ . The same sequences are reproduced with J ₂ closed and J ₁ , J ₃ open, then J ₃ closed and J ₁ , J ₂ open, so that all of the photoconductors of the mosaic flow successively through the resistor R ₁ .

Reading to the next line is then carried out either by moving the image of the diaphragm slot 103 by a step-by-step movement of the motors 104 or 135, or by moving the document itself by a stepping movement of the motor 151; in this case, contrary to what is shown in FIG. 1, the translation of the positioning means 15 takes place in the plane of the figure, parallel to the common optical axis of the objectives 102 and 131. As soon as the translation is carried out , the same reading cycle of the photo-detectors of the mosaic 12 is repeated. These alternating actions: point-by-point reading of a line-translation to the next line, are repeated until the page is fully read.

FIGS. 7a and 7b relate to the receiving part of the facsimile machine and respectively show the arrangement of the heating resistors and the electrodes on the internal faces of the blades 20 and 21, as well as the diagram of the connections intended to control them.

FIG. 7a represents, in a simplified version, the configuration of the transparent conductive deposits arranged on the internal face of the blade 20. These deposits form Q = 3 distinct resistors 31, 32 and 33, placed end to end and covering the entire surface of the diaphragm slot 103; the latter is arranged as in the first embodiment, and in accordance with FIG. 2a, on the external face of this same blade. Each resistor has one of its terminals connected to ground; the three other terminals lead to three separate lines 301, 302 and 303, conveying the heating pulses I _C1 , I _C2 and I _C3 coming from the heating pulse generator 190.

FIG. 7b represents, still in the same simplified version, the transparent conductive deposits arranged on the internal face of the blade 21 to act as electrodes 3ij. To facilitate understanding of the device, the resistors 31, 32 and 33 which make them opposite have been, in this same figure, represented in punctuated lines. The cell has Q = 3 sets (or groups) of P = 4 identical electrodes. The electrodes of the same set, for example the electrodes 321 to 324, are arranged opposite the same resistance in this case the electrode 32. The dimensions and the pitch of the electrodes are identical to the dimensions and to the not sensitive surfaces of the photo-detectors comprising the linear mosaic, represented by FIG. 6.

The row j electrodes of the 3 sets: 31j, 32j and 33j are connected to a common line 34j, connected to one of the output terminals of the series-parallel converter 182 to receive the control voltage pulses V _cj ; thus the three row 3 electrodes: 313, 323 and 333 are connected to the single line 343 to receive the pulses V _c3 .

The inscription of a row of row n on the photosensitive surface 14 is carried out as follows. The starting point will be the moment when the row of rank n - 1, entered in cell 11 in the form of P x Q separate points (i.e. 12 points in the case of the simplified version described in Figures 6, 7a and 7b ) has just been projected onto the surface 14. The heating pulses I _C1 , I _C2 , I _C3 all have the same duration t, and follow one another at the frequency 1 / t ,. The heat given off by each pulse in the corresponding resistor momentarily carries the adjacent portion of layer 3 in the isotropic phase and erases the information which was previously recorded there.

The duration t, of the first heating pulse Here applied to the resistor 31 is used to move the spacing between two consecutive lines or the image projected on the surface 14 by a step-by-step movement of the motors 106 to 135, or the photosensitive surface 14 itself by a step-by-step movement of the motor 143, according to the chosen version of the device. While the second heating pulse I _C2 is applied to the resistor 32, the series-parallel converter 182 simultaneously applies, for a time t ₁ , to the four lines 341 to 344 the control voltage pulses V _C1 to V _C4 , which are, in order, the first four pulses sampling the video signal corresponding to the start of line n. The same signal, V _C1 for example, is thus applied to three different electrodes: 311, 321 and 331; but only the voltage applied to the electrode 311 modifies the optical properties of the adjacent portion of the layer 3; indeed, only the portion of the layer 3 facing the resistor 31 is in the stage of cooling from the liquid phase to the smectic phase. The first four signals are thus recorded only in the portions of layer 3 comprised between the heating resistor 31 and the electrodes 311 to 314. As previously explained, the recording is done in the form of variations in the diffusion coefficient, the diffusion being d 'all the more pronounced as the control voltage pulse is weaker and is maintained as long as the element is not again brought to the liquid phase.

• - d'une part, à l'impulsion de tension d'ordonner éventuellement les molécules du matériau mésomorphe afin de contrecarrer, lors du refroidissement pendant la transition nématique-smectique, l'établissement spontané d'un état désordonné diffusant ;
• - et d'autre part, un refroidissement suffisant de la couche interdisant aux impulsions de tension ultérieures d'exercer leur action orientatrice.

More generally, the P control pulses simultaneously delivered by the converter 182 to all of the electrodes during the duration of the heating pulse applied to the resistor 3j act on the liquid crystal at the sole level of the resistor 3 (d - 1). The time t ₁ must be sufficient to allow:

• - on the one hand, the voltage pulse to possibly order the molecules of the mesomorphic material in order to counteract, during cooling during the nematic-smectic transition, the spontaneous establishment of a disordered diffusing state;
• - And on the other hand, sufficient cooling of the layer preventing subsequent voltage pulses from exerting their orienting action.

Values of t, of the order of 0.5 ms, meet this double imperative when using the C.O.B. cited above as a mesomorphic material with a thickness of about ten microns.

When the entire line has been recorded according to the process described above, process which required the time Qt, (ie 3t, in the simplified version described), the modulator 104 lets the source 100 appear for a sufficient time t ₂ to allow the photo-sensitive layer 14 to record the line n intermediately displayed by the cell 11. An identical cycle is then repeated for the recording of the row of rank n + 1.

As an example of application of this second type of embodiment of the device according to the invention, the width l ₁ = 60 μm and the length 1 ₂ = 52.5 mm, l are adopted for the diaphragm slot 103 objective 131 working at magnification 4. The heating resistors are Q = 36, spaced 5 μ from each other and have a value R = 10 n. At each resistance are superimposed P = 48 electrodes of 65 µm by 25 µm, spaced from each other by 5 µm. A 21 cm x 27 cm page is thus reproduced in the form of 1,200 lines of P x Q = 1,728 points each, by a cell requiring only P + Q = 84 entries.

By adopting for t, a value of 0.5 ms, and for t ₂ a value of 1 ms, the total duration of inscription of a line is 19 ms, that is to say 23 s for the inscription of a page. Referring to the average sensitivity characteristics of heat-developable silver-coated papers, it can be seen that a source of tungsten filament lamp whose power is of the order of 50 watts can be used for source 100. The average power dissipated by the resistive elements of the cell is around 30 mwatts.

Without departing from the scope of the present invention, it is possible to disperse within the mesomorphic material particles having a preferred direction of light absorption and the orientation of which is controlled by that of the mesomorphic material, in accordance with the patent application. in France, filed on December 3, 1976 by the Applicant under the national registration number 76 36 532 and entitled: “Liquid crystal cell •. Variations in the diffusion coefficient of the layer mesomorph 3 are then reinforced by variations in absorption coefficient, which makes it possible to work with objectives 102 and 131 which are more open and to eliminate the diaphragm 132.

Claims (4)

1. Telecopying method for generating a video signal transcribing a document to be reproduced and for providing a copy of this document upon reception of this signal ; the video signal resulting from an analysis of the document by successive segments of N points using photodetector means ; the copy being obtained by an alternating succession of intermediate inscription and final inscription steps ; the intermediate inscription being performed by a thermo-optic method in a layer (3) comprising a mesomorphous material presenting a smectic phase, and the final inscription resulting from the projection of this intermediate inscription onto photosensitive means (14) ; this method being characterized in that said layer having the form of a rectilinear strip, the intermediate inscription step comprises storing of said segments of N points over the length of this strip in the form of Q successive adjacent sub- segments of P simultaneous points ; P, Q and N being integers, P and Q exceeding unity and being at least equal to unity, respectively, and the product P x Q being equal to N : the storing of one sub-segment being preceded by the momentary simultaneous heating of P points of the corresponding portion of said strip for heating the mesomorphous material from its smetic phase to its isotrope liquid phase, during which any previously stored element is erased from said portion, and being subsequently obtained by submitting said same portion, during its subsequent cooling to the initial temperature, to P simultaneous control voltage pulses representing the received signal ; the final inscription step comprising the simultaneous projection of the N points momentarily inscribed into the layer.

2. Receiver-transmitter telecopier for performing the method in accordance with claim 1, characterized in that it comprises :

- said layer (3) comprising a mesomorphous material presenting a smectic phase and sandwiched between two transparents plates (20 and 21) ;

- Q identical, transparent, rectilinear and aligned resistive elements (3i) arranged on the inner face of one of the plates, each for momentarily heating the facing portion of the layer from a first temperature where the mesomorphous material is in its smectic phase to a second temperature where it is in said isotrope liquid phase under the action of a heating pulse ;

- Q groups each of P identical and transparent control electrodes (3ij) aligned on the inner face of the other plate, each group facing one of the resistive elements ;

- heating pulse generator means (190) delivering sequences of Q identical heating pulses of fixed period and constant frequency and for addressing the pulses of the same sequence successively to each of the resistive elements ;

- control pulse generator means (180, 181 and 182) for storing said video signal in successive groups of P successive points and for restitution of said signal in the form of sequences having the same period as the heating pulse sequences, each sequence comprising Q successive groups of said P simultaneous control voltage pulses ; these pulses having the same frequency as the heating pulses ; the control pulse of the order i of the same group being simultaneously delivered to each electrode of the order i of the Q control electrode groups ;

- control means (16) acting upon the heating pulse and the control pulse generator means in order that the control pulse sequence of the order n be delivered with a constant delay with respect to the heating pulse sequence of the same order, said delay being at least equal the duration of one heating pulse, and that a constant time gap separates the end of the control pulse sequence of the order n from the beginning of the heating pulse sequence of the order n + 1 ;

- illuminating means (100, 101 and 102) for projecting a light flow onto the layer during said time gap ;

- projection means (131) for receiving at least part of this light flow after its crossing of the layer and for forming an image of the latter ;

- photosensitive means (14) for storing this image, and

- moving means (140, 141,142,143) for assuring the reiative movement of this image with respect to the photosensitive means.

3. Telecopier in accordance with claim 2, characterized in that the illumination means (100, 101 and 102) and the projection means (131) are adapted to be used for projecting an image of part of the document to be transmitted upon said photodetector means, the latter being formed by a linear mosaic (12) of photoelectric detectors (121, 122, ..., 128).

4. Telecopier in accordance with claim 2, characterized in that the mesomorphous material contains dispersed particles of a second material having a preferential direction of light absorption and the orientation of which is controlled by that of the mesomorphous material.

Images